1. Field of the Invention
The present invention relates to a scroll type refrigerant compressor, and more particularly relates to an improvement in the counterweight means and a drive bushing member accommodated therein.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 2-176179 discloses a typical scroll type refrigerant compressor provided with a stationary scroll unit fixedly encased in a housing means, and a movable scroll unit orbiting in the housing means so as to compress refrigerant gas in cooperation with the stationary scroll unit. The stationary scroll unit includes a stationary spiral member and an end plate member fixedly attached to an end of the spiral member and to the housing means. The stationary spiral member is formed as a wall member extending spirally along an involute curve with respect to a given point, i.e., a center of the stationary spiral member.
The movable scroll unit includes a movable spiral member engaged with the stationary spiral member and a movable end plate member fixed to an end of the movable spiral member on the side axially opposite to the end plate member of the stationary scroll unit. The movable spiral member, which is also formed as a wall member extending spirally along an involute curve with respect to a given point, i.e., a center of the movable spiral member is arranged so as to be circumferentially shifted from the stationary spiral member by 180.degree..
The scroll type refrigerant compressor is also provided with an axial drive shaft rotatably supported in the housing means and having a large diameter portion formed at an end thereof. The large diameter portion of the drive shaft is provided with an integral drive key member projecting axially from the end face thereof. The drive key member is formed as a part-cylindrical member having a central axis thereof radially shifted from the center of rotation of the drive shaft. The drive key member is provided with opposite planar faces extending in parallel with the central axis and two diametrically opposed circular faces. The planar faces of the drive key member are arranged on opposite sides with regard to a diametrical axis of the key member which extends perpendicularly to the above-mentioned central axis. The diametrical axis of the drive key member is inclined from a predetermined diametrical axis passing therethrough the axis of rotation of the drive shaft and the central axis of a later-described drive bushing member.
The axial drive shaft is also provided with a counterweight substantially integral with the large diameter portion of the drive shaft. The above-mentioned bushing member is provided with an aperture into which the part-cylindrical drive key member of the drive shaft is inserted in a manner such that the drive key member is able to slide in the diametrical axis thereof. The bushing member is engaged with the movable spiral member of the movable scroll unit via a bearing element so as to move the movable scroll unit in an orbiting path with regard to the stationary scroll unit. The movable scroll unit is, however, prevented from being rotated about the central axis thereof by an appropriate rotation preventing means such as described in U.S. Pat. No. 4,824,346.
The principle of operation of the described scroll type refrigerant compressor is well known. Namely, the rotation of the drive shaft is converted into the orbiting motion of the movable scroll unit in relation to the stationary scroll unit via the drive key member, the drive bushing member and the rotation preventing unit, and as a result, a gradual shifting of lines of contact between the spiral member of the stationary scroll unit and that of the movable scroll unit from radially outer portions of both units toward radially central portions of both units occurs. Therefore, refrigerant pockets are successively formed between the stationary scroll unit and the movable scroll unit and shifted gradually toward the center of both units while the volume thereof is reduced. Consequently, the refrigerant gas introduced initially through a refrigerant inlet port of the compressor into the refrigerant pockets is gradually compressed and eventually discharged from the refrigerant pockets toward a discharge chamber of the compressor via an outlet port formed in the end plate member of the stationary scroll unit.
During the orbiting motion of the movable scroll unit, the counterweight arranged around the drive shaft acts against a moment to which the bushing member is subjected due to the orbiting motion of the movable scroll unit to thereby absorb a dynamic unbalance acting on the bushing member.
Further, the drive bushing member is able to slide with respect to the drive key member of the drive shaft in the direction of the afore-mentioned diametrical axis of the drive key member so as to adjust the line contacts between the stationary and movable scroll units. Namely, when the drive bushing member is shifted toward a position increasing an amount of eccentricity with regard to the rotating center of the drive shaft, the radius of orbiting motion of the movable scroll unit is increased. Namely, the movable scroll unit is urged against the stationary scroll unit, and accordingly, a sealing of the refrigerant pockets in which the refrigerant gas is compressed is occurs.
The drive bushing member can be also shifted in the opposite direction to the above-mentioned eccentricity-increasing direction so as to decrease an amount of eccentricity thereof with regard to the rotating center of the drive shaft. Thus, it is possible to absorb a slight misalignment in the engagement of the stationary and movable scroll units as well as to avoid a collision of both units which occurs when the rotating direction of the compressor is reversed at the moment of stopping of the compressor or when any foreign materials enter into the interior of the compressor.
Nevertheless, in the above-described conventional scroll type refrigerant compressor, the aperture of the drive bushing member is formed as a through-hole, and the drive key member of the drive shaft is inserted in the through-hole type aperture of the bushing member in such a manner that an extreme end of the drive key member is projected from the aperture. A retaining ring element such as a conventional circular snap ring is attached to the extreme end of the drive key member to prevent withdrawal of the drive key member from the drive bushing member. However, the retaining ring is insufficient for preventing an uncontrolled movement of the drive bushing member with respect to the drive key member of the drive shaft. More specifically, since a given amount of axial spacing is left between the retaining ring or circular snap ring attached to the extreme end of the drive key member of the drive shaft and the end face of the drive bushing member, and since the aperture of the bushing member is formed so as to permit the sliding movement of the bushing member, the drive bushing member is uncontrollably inclined from a plane perpendicular to the axis of rotation of the drive shaft with respect to the drive key member of the drive shaft. Accordingly, the movable scroll unit operatively engaged with the drive bushing member must orbit at a posture thereof inclined away from a normal condition. Therefore, there occurs local abrasion of the stationary and movable scroll units during the operation of the compressor. Also, noise can be generated during orbiting of the movable scroll, due to the incorrect engagement of the scroll units.
Nevertheless, if the axial spacing between the retaining ring of the drive key member of the drive shaft and the end face of the drive bushing member is sufficiently reduced to prevent the above-mentioned local abrasions and generation of the noise, the drive key member of the drive shaft is unable to smoothly slide in the aperture of the drive bushing member to thereby cause a problem of incomplete radial sealing between the stationary and movable scroll units. Moreover, a minute positional discrepancy between the stationary and movable scroll units cannot be absorbed.